1. Field of the Invention
This invention relates in general to transmissions for self propelled vehicle or rotating machinery use and in particular to high efficiency all mechanical continuously variable ratio transmissions.
2. Prior Art
The need for a high efficiency, continuously variable ratio (CVR) transmission, or mechanical impedance transformer, has been well recognized in the motor vehicle industry and to a lesser extent throughout the industrial machine community. The potential usefulness of such a device in the automobile has increased greatly with the introduction of the on-board microprocessor, since the type of sophisticated control required to fully exploit such a transmission is now easily available.
The limitations of presently employed types of transmissions are well known and therefore are only briefly described below. Mechanical gear train types are the lowest loss but offer only discrete torque vs. speed ratios and are thus only approximating an optimum match from engine to load. Hydraulic torque converter transmissions are relatively high loss as demonstrated by the oil coolers associated with them. Other types of lower power handling mechanical transmissions, which may incorporate a continuously variable ratio feature, all depend on a friction surface coupling which immediately introduces losses, wear rate problems and maximum power transfer limitations.
All presently employed types of transmissions are based on the use of either the lever arm or the inclined plane basic machines of physics. For the lever arm types, changing speed-torque ratios means changing input to output lever arm ratios. With one known exception, these lever arm changes employ friction surface couplings with all of the basic limitations described above. The exception is U.S. Pat. No. 4,660,427 which employs a sequence of meshed gear couplings. However, this concept is intrinsically complex, fragile and capable of one way power flow only.
For the inclined plane types, changing speed-torque ratios means changing the tilt angle of a rotating element, such as the well known swash plate used in many positive displacement hydraulic type transmissions. All of these hydraulic transmissions suffer from fluid flow friction losses and are therefore not suitable for high efficiency, controllable ratio applications. U.S. Pat. No. 4,763,544 also uses the swash plate together with oscillating pawls to achieve an all mechanical type transmission. However, this implementation is also complex, fragile and limited to one way power flow.